U.S. patent application number 10/743978 was filed with the patent office on 2004-09-30 for on-line control of coal flow.
Invention is credited to Aliy, Elshabasi, Bilirgen, Harun, Levy, Edward Kenneth.
Application Number | 20040188554 10/743978 |
Document ID | / |
Family ID | 32994101 |
Filed Date | 2004-09-30 |
United States Patent
Application |
20040188554 |
Kind Code |
A1 |
Levy, Edward Kenneth ; et
al. |
September 30, 2004 |
On-line control of coal flow
Abstract
A system for balancing and controlling the distribution of
pulverized coal into multiple equal diameter outlet pipes of coal
pulverizers for improving boiler performance. The device includes a
plurality of flow control elements, one flow control element for
each outlet pipe, all positioned a pre-determined distance upstream
of the outlet pipes. Each flow control element is mounted on an
independent adjustment mechanism and is thereby adjustable in
position relative its corresponding outlet pipe to selectively vary
the wake of the downstream coal particulate flow relative to
primary air flow. The method of the present invention is practiced
by monitoring coal particulate flow at the outlet pipes relative to
primary air flow or individual flame characteristics, and then
compensating for noted imbalances by selectively adjusting the flow
control elements, thereby balancing and controlling the
distribution of coal and improving combustion efficiency.
Inventors: |
Levy, Edward Kenneth;
(Bethlehem, PA) ; Bilirgen, Harun; (Bethlehem,
PA) ; Aliy, Elshabasi; (Bethlehem, PA) |
Correspondence
Address: |
ROYAL W. CRAIG
SUITE 153
10 NORTH CALVERT STREET
BALTIMORE
MD
21202
US
|
Family ID: |
32994101 |
Appl. No.: |
10/743978 |
Filed: |
December 23, 2003 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60436241 |
Dec 26, 2002 |
|
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|
Current U.S.
Class: |
241/119 |
Current CPC
Class: |
B02C 15/00 20130101;
B07B 7/08 20130101; B02C 2015/002 20130101 |
Class at
Publication: |
241/119 |
International
Class: |
B02C 023/32 |
Claims
We claim:
1. In a vertical coal pulverizer having a discharge turret and
plurality of pulverized coal outlet pipes in said discharge turret,
a device for balancing and controlling the distribution of
pulverized coal into the plurality of outlet pipes comprising: a
plurality of adjustable flow control elements positioned within
said discharge turret of said pulverizer, each of said plurality of
flow control elements corresponding to one of said plurality of
outlet pipes and being spaced there from, a corresponding plurality
of adjustment mechanisms for each of said plurality of flow control
elements for adjusting the position of the flow control element
relative to said corresponding outlet pipe.
2. The device for balancing and controlling the distribution of
pulverized coal into the plurality of outlet pipes of claim 1,
wherein the shape of each flow control element is aerodynamic to
induce a wide coal particle concentration wake and a narrow primary
air flow wake relative to said coal particle concentration
wake.
3. The device for balancing and controlling the distribution of
pulverized coal into the plurality of outlet pipes of claim 2,
wherein said plurality of flow control elements are each positioned
an equal predetermined distance upstream of the entrance to said
outlet pipes.
4. The device for balancing and controlling the distribution of
pulverized coal into the plurality of outlet pipes of claim 3,
wherein said predetermined distance comprises a function of the
diameter of said outlet pipes and the structure and configuration
of said pulverizer including the number of outlet pipes.
5. The device for balancing and controlling the distribution of
pulverized coal into the plurality of outlet pipes of claim 2,
wherein said each of said aerodynamic flow control elements
comprises a convex rounded windward end, smooth tapering sides and
a pointed leeward end.
6. The device for balancing and controlling the distribution of
pulverized coal into the plurality of outlet pipes of claim 5,
wherein the convex rounded windward end has a diameter that is a
function of the diameter of said outlet pipes and the structure and
configuration of said pulverizer including the number of outlet
pipes.
7. The device for balancing and controlling the distribution of
pulverized coal into the plurality of outlet pipes of claim 6,
wherein said flow control elements have a length that is a function
of the diameter of said outlet pipes and the structure and
configuration of said pulverizer including the number of outlet
pipes.
8. The device for balancing and controlling the distribution of
pulverized coal into the plurality of outlet pipes of claim 1,
wherein each of said flow control elements is mounted on and
supported by said corresponding adjustment mechanism, and said
corresponding adjustment mechanism allows for independent
adjustments of the position of each flow control element relative
to the center point of said corresponding outlet pipe in order to
selectively vary the particle concentration wake to alter the
concentration of the pulverized coal flow into the corresponding
outlet pipe, the closer the flow control element is to being
aligned with the center point of the outlet pipe, the lesser the
concentration of the pulverized coal flowing into the outlet
pipe.
9. The device for balancing and controlling the distribution of
pulverized coal into the plurality of outlet pipes of claim 8,
wherein each of the plurality of adjustable flow control elements
is pre-positioned inside said discharge turret of said pulverizer
at said predetermined distance upstream of the entrance to said
outlet pipes allowing a free flow of pulverized coal into the
outlet pipes; and wherein the position of each of the plurality of
adjustable flow control elements may be adjusted from said
preposition using said adjustment mechansim.
10. The device for balancing and controlling the distribution of
pulverized coal into the plurality of outlet pipes of claim 9,
wherein said adjustment mechanism is accessible on-line from
outside said pulverizer.
11. The device for balancing and controlling distribution of
pulverized coal into the plurality of outlet pipes of claim 10,
wherein each adjustment mechanism is comprised of a support rod
attached to a corresponding flow control element; each of said
support rods is further mounted in a sealed bushing in the
discharge turret such that each rod is accessible on-line from
outside said pulverizer and may be rotated or slid back and forth
within its bushing to adjust the position of the attached flow
control element relative its corresponding outlet pipe.
12. The device for balancing distribution of coal among the outlet
pipes according to claim 1, further comprising a plurality of
orifice flow restrictors each located in a corresponding outlet
pipe.
13. The device for balancing and controlling distribution of
pulverized coal into the plurality of outlet pipes of claim 1,
wherein said pulverizer is a pressurized vertical spindle
pulverizer with four pulverized coal outlet pipes, the diameter of
the convex rounded windward end of said flow control elements is
approximately equal to one-quarter the diameter of said pulverized
coal outlet pipes, the length of said flow control elements is
approximately equal to one half the diameter of the pulverized coal
outlet pipes and the distance between the entrance to each of the
four outlet pipes and its corresponding flow control element is
optimal at approximately two times the outlet pipe diameter.
14. The device for balancing and controlling distribution of
pulverized coal into the plurality of outlet pipes of claim 1,
wherein said device is adapted for after-market installation.
15. In a vertical coal pulverizer that produces pulverized coal for
use as boiler fuel of a type having a raw coal inlet port and
chute, a coal grinding mechanism, primary air flow as a means for
transporting pulverized coal, a discharge turret and a plurality of
pulverized coal outlet pipes of equal diameter, a method for
balancing and controlling the distribution of pulverized coal into
the plurality of outlet pipes and thereby improving boiler
performance; said method comprising the steps of: monitoring
distribution of pulverized coal flow into each of said outlet pipes
relative to primary air flow; and compensating for imbalances in
said pulverized coal flow into said outlet pipes by positioning
flow control elements corresponding to each outlet pipe a
predetermined distance upstream from said outlet pipes and
selectively adjusting the individual flow elements on-line in order
to alter the rate of pulverized coal flow into said corresponding
outlet pipes.
16. The method of claim 15, wherein the step of monitoring
distribution of pulverized coal flow into each of said outlet pipes
relative to a primary air flow is accomplished by measuring a
concentration of pulverized coal flow at the individual pulverized
coal outlet pipes.
17. The method of claim 15, wherein the step of monitoring
distribution of pulverized coal flow into each of said outlet pipes
relative to primary air flow is accomplished by measuring
particular flame characteristics of burning fuel discharged from
the each of the outlet pipes.
18. The method of claim 15, wherein adjusting a flow control
element is accomplished by selectively changing the position of the
flow control element relative to the center point of the entrance
to its corresponding outlet pipe, the closer the flow control
element is to being aligned with the center point of the outlet
pipe, the lesser the concentration of the pulverized coal flowing
into the outlet pipe.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] The present application derives priority from U.S.
Provisional Patent Application 60/436,241 for "ON-LINE CONTROL OF
COAL FLOW IN PRESSURIZED VERTICAL SPINDLE MILLS" filed by Levy et
al. on Dec. 23, 2002.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to coal pulverizers and, more
particularly, to the on-line control of the distribution of coal
among the pulverized coal outlet pipes in pulverizers using
independently adjustable flow control elements installed inside the
pulverizer upstream of the entrance to each pulverized coal outlet
pipe.
[0004] 2. Description of the Background
[0005] Coal fired boilers utilize pulverizers to grind coal to a
desired fineness so that it may be used as fuel for the boilers.
Typically, raw coal is fed through a central coal inlet at the top
of the pulverizer and falls by gravity to the grinding area. Once
ground (different types of pulverizers use different grinding
methods), the pulverized coal is transported upwards, using air as
the transport medium. The pulverized coal passes through classifier
vanes within the pulverizer. These classifier vanes may vary in
structure, but are intended to establish a swirling flow within the
rejects cone to prevent coarse coal particles from flowing into the
discharge turret of the pulverizer. These vanes are often
adjustable mechanisms. The centrifugal force field set up in the
rejects cone forces the coarse coal particles to drop back down
onto the grinding surface until the desired fineness is met. Once
the coal is ground finely enough, it enters the discharge turret.
From the discharge turret the pulverized coal is distributed among
multiple pulverized coal outlet pipes and into respective fuel
conduits where it is carried to the burners. Each coal pulverizer
is an independent system and delivers fuel (pulverized coal) to a
group of burners.
[0006] Poor balance of pulverized coal distribution between
pulverized coal outlet pipes is commonly experienced in utility
boilers. This can be due to various reasons, such as system
resistance of each individual fuel conduit, physical differences
inside the pulverizer, and coal fineness. Unbalanced distribution
of coal among the pulverized coal outlet pipes adversely effects
unit performance and leads to decreased combustion efficiency,
increased unburned carbon in fly ash, increased potential for fuel
line plugging and burner damage, increased potential for furnace
slagging, and irregular heat release within the combustion chamber.
In addition, it is critical for low NO.sub.x (Nitric Oxides) firing
systems to precisely control air-to-fuel ratios in the burner zones
to achieve low levels of NO.sub.x formation.
[0007] Therefore, there is a need in the industry for a method and
apparatus that provides for on-line balance and control of the
distribution of pulverized coal between the multiple pulverized
coal outlet pipes of coal pulverizers.
SUMMARY OF THE INVENTION
[0008] Accordingly, it is the main object of the present invention
to provide an improved method and apparatus for the on-line
balancing and control of pulverized coal flow into the multiple
pulverized coal outlet pipes of a coal pulverizer, thereby
improving boiler performance by making it possible to operate the
boiler with reduced pollutant levels (e.g. NO.sub.x, CO) and
increased combustion efficiencies.
[0009] It is another object of the present invention to provide an
improved method and apparatus for the on-line balancing and control
of pulverized coal flow from the discharge turret of a coal
pulverizer into multiple pulverized coal outlet pipes and onto
connected fuel conduits that does not disturb any pre-existing
primary air flow balance among the multiple pulverized coal outlet
pipes.
[0010] It is a further object of the present invention to provide
an improved method and apparatus for the on-line balancing and
control of pulverized coal flow from the discharge turret a coal
pulverizer into multiple pulverized coal outlet pipes, where the
type of pulverizer is a pressurized vertical spindle pulverizer. It
is a further object of the present invention that the apparatus can
be readily installed within an existing pressurized vertical
spindle pulverizer without causing a significant pressure drop.
[0011] The objects of the present invention are accomplished by
providing a device for balancing and control of pulverized coal
distribution to multiple pulverized coal outlet pipes of a coal
pulverizer. The device generally comprises a plurality of
independently adjustable flow control elements and a means for
adjusting the positioning of those flow control elements.
[0012] It is a further object of the present invention that each of
the multiple flow control elements corresponds to an outlet pipe
and controls the flow of pulverized coal into that particular
corresponding outlet pipe.
[0013] It is a further object of the present invention that each of
the multiple flow control elements is positioned within the
discharge turret of the coal pulverizer at some appropriate
distance upstream from the entrance to its corresponding pulverized
coal outlet pipe.
[0014] Yet another object of the present invention is to provide a
means for independently adjusting the positioning of each of the
multiple flow control elements within the discharge turret and
thereby, controlling the flow of pulverized coal to the
corresponding outlet pipe.
[0015] It is a further object of this invention that each
adjustment mechanism includes an independently adjustable rod
seated in the top or side of the discharge turret of the coal
pulverizer and connected to the flow control element for adjusting
positioning of the flow control element horizontally or
vertically.
[0016] The method of the present invention is practiced by
monitoring either the pulverized coal flow at the individual
pulverized coal outlet pipes or the individual flame
characteristics, and then compensating for imbalances in the coal
particulate flow or differences between flame characteristics by
selectively adjusting the individual flow control elements as
needed, thereby balancing and controlling the distribution of
pulverized coal and improving combustion efficiency.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] Other objects, features, and advantages of the present
invention will become more apparent from the following detailed
description of the preferred embodiment and certain modifications
thereof when taken together with the accompanying drawings in
which:
[0018] FIGS. 1A and 1B are illustrations of an exemplary prior art
coal pulverizer with multiple fuel conduits and a medial vertical
cross section of this exemplary coal pulverizer, respectively
[0019] FIGS. 2A and 2B are a horizontal cross section of the
discharge turret and a medial vertical cross section of the
pulverizer, respectively, of the preferred embodiment of the
present invention.
[0020] FIGS. 3A and 3B each illustrate the particle concentration
and air velocity distributions for a different positioning of an
exemplary flow control element within a horizontal plane relative
to the entrance to the corresponding pulverized coal outlet
pipe.
[0021] FIG. 4 is a cross-section illustration of the air flow over
an exemplary flow control element of the present invention.
[0022] FIG. 5 is a comparative graph showing the percentage of
pulverized coal flow imbalance with and without the flow control
elements in each outlet pipe.
[0023] FIG. 6 is a comparative graph showing the effect of coal
flow balancing with and without the flow control elements on
primary airflow distribution in each outlet pipe.
[0024] FIG. 7A-B illustrate exemplary, fixed and adjustable,
orifice plates.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0025] In a conventional coal pulverizer 100 (as shown in FIGS.
1A-1B and FIG. 2) raw coal 101 is dropped into coal inlet port 102
and by force of gravity falls through coal chute 103 until it
reaches the grinding mechanism 104. The grinding mechanism 104
grinds the coal into fine pieces. Air 105 flows into air inlet port
106 and transports the pulverized coal 107 upwards towards the
inverted cone-shaped discharge turret 108. Typically, the
pulverized coal 107 passes through a classifier vane mechanism 109
that establishes a swirling flow within the rejects cone 120. The
centrifugal force field set up in the reject cone 120 prevents
coarse pieces of coal 110 from entering the discharge turret 108.
The coarse pieces of coal 110 fall by force of gravity back into
the grinding mechanism 104. Once the pulverized coal 107 enters the
discharge turret 108 it is distributed between the multiple equal
diameter pulverized coal outlet pipes 111 (FIG. 1 indicates six
pulverized coal outlet pipes 111). The pulverized coal 107 is then
carried by connected fuel conduits to a boiler where it is burned
as fuel.
[0026] As discussed above, poor balance of pulverized coal 107
distribution between pulverized coal outlet pipes 111 is commonly
experienced in utility boilers. This can be due to various reasons,
such as system resistance of each individual fuel conduit, physical
differences inside the pulverizer, and coal fineness. The
unbalanced distribution of coal among the pulverized coal outlet
pipes adversely affects the unit performance and leads to decreased
combustion efficiency, increased unburned carbon in fly ash,
increased potential for fuel line plugging and burner damage,
increased potential for furnace slagging, and non-uniform heat
release within the combustion chamber. In addition, it is critical
for low NO.sub.x (Nitric Oxides) firing systems to precisely
control air-to-fuel ratios in the burner zones to achieve minimum
production of NO.sub.x. The relative distribution of coal between
the pulverized coal outlet pipes is monitored by either measuring
the concentration of pulverized coal flow at the individual
pulverized coal outlet pipes or measuring the particular flame
characteristics of burning fuel discharged from the each of the
outlet pipes.
[0027] The method and apparatus of the present invention represent
an improvement over the prior art of FIGS. 1A-B. Specifically, the
invention described herein is a system, inclusive of method and
apparatus, for the on-line balance and control of the flow of
pulverized coal from the discharge turret of a coal pulverizer into
its multiple pulverized coal outlet pipes. The preferred embodiment
of the present invention is described herein for application in a
conventional pressured vertical spindle mill type pulverizer (as
shown in FIGS. 1A-B). This type of pulverizer operates at pressures
above atmospheric pressure and employs a rotating horizontal
grinding table and a multiplicity of grinding elements to pulverize
the coal. Typically, pressurized vertical spindle mill type
pulverizers have 3 to 8 pulverized coal outlet pipes 111. However,
those skilled in the art will appreciate that this invention may be
applied to other similarly structured vertical coal pulverizers of
a type having a raw coal inlet port and chute, a coal grinding
mechanism, air flow as a means for transporting pulverized coal,
classifier vanes, a discharge turret and multiple pulverized coal
outlet pipes connected to fuel conduits.
[0028] Referring to FIGS. 2A and 2B, the apparatus of the present
invention comprises a plurality of individually adjustable flow
control elements 10 located inside the discharge turret 108 of a
coal pulverizer 2. The number of flow control elements 10 is equal
to the number of pulverized coal outlet pipes 111 and each flow
control element 10 corresponds to a particular pulverized coal
outlet pipe 111. FIGS. 2A and B, show a pulverizer 2 with four
outlet pipes 111. Each of the plurality of flow control element 10
is positioned inside the discharge turret 108 at some predetermined
distance from the entrance 112 to the pulverized coal outlet pipes
111.
[0029] Generally, each flow control element 10 will be positioned
in a horizontal plane at some point directly below (upstream of)
the pulverized coal outlet pipes 111, allowing a free flow of
pulverized coal into the outlet pipes 111. However, the horizontal
and vertical positioning of each individual flow control element 10
may be adjusted by a flow control adjustment mechanism 20 to align
the flow control element 10 to some degree in front of the entrance
112 to the corresponding pulverized coal outlet pipe 111 in order
to decrease the flow of pulverized coal 107 into that particular
outlet pipe 111.
[0030] The working principle of adjusting pulverized coal flow
balance, by adjusting the positioning of the individual flow
control elements 10 relative to the entrance 112 of the particular
outlet pipes 111 is based upon creating a pulverized coal particle
concentration wake 115 just upstream of each outlet pipe 111 that
receives a relatively high pulverized coal particle flow rate (see
FIGS. 3A and 3B). The distance (d) between the flow control
elements 10 and the entrance to the outlet pipes 112 and the shape
and dimensions of the flow control elements 10 are optimized in
such a way that the distribution of pulverized coal 107 into the
pulverized coal outlet pipes 111 is balanced while the effect of
the flow control elements 10 on the primary air flow distributions
116 (See FIGS. 3A and B) is negligible. This balance improves
boiler performance by increasing combustion efficiency, decreasing
unburned carbon in fly ash, decreasing potential for fuel line
plugging, burner damage and furnace slagging, and more uniformly
releasing heat within the combustion chamber. The optimal distance
for positioning the flow control elements within the discharge
turret of a particular coal pulverizer must be determined by
experimentation either in the field or in a laboratory setting or
by mathematical calculations because different coal pulverizer
designs have different internal proportions which effect both
outflow coal and air distributions. This distance is proportional
to the diameter of the outlet pipes. Similarly, the optimal shape
and dimensions of the flow control elements also depend upon the
internal proportions of the particular coal pulverizer. In
practice, adjusting a flow control element such that it is
positioned under the pulverized coal outlet pipe, decreases the
flow of pulverized coal into the outlet pipe. Adjusting a flow
control element such that it is shifted some distance to the side
relative to the pulverized coal outlet pipe, increases the flow of
pulverized coal into the outlet pipe.
[0031] FIGS. 3A and 3B illustrate the pulverized coal particle
concentration and air velocity distributions, respectively,
downstream of an exemplary streamlined flow control element 10 for
two different positions of the flow control element. Since the
pulverized coal particles 107 have more inertia than the air, the
particle concentration wake (Wp) 115 is considerably wider than the
air flow distribution wake (Wa) 116 at the entrance 112 to the
corresponding outlet pipe 111. When a flow control element 10 is
adjusted such that the center of the pulverized coal particle
concentration wake 115 is lined up with the outlet pipe centerline,
a reduction in pulverized coal particle flow into the corresponding
pipe occurs (FIG. 3A). On the other hand, when the flow control
element is adjusted so that it is positioned to one side of the
outlet pipe 111, the highly concentrated particle flow stream
created at the edge of the particle concentration wake is directed
towards the entrance 112 of the of the corresponding outlet pipe
111 resulting in an increase in pulverized coal flow 107 into the
outlet pipe (FIG. 3B). Since each flow control element 10 is
independently adjustable, the coal flow rates in each pipe can be
adjusted using techniques similar to that explained above.
[0032] Those skilled in the art will recognize that a variety of
adjustment mechanisms 20 are suitable for supporting the individual
flow control elements 10 within the discharge turret 108 and for
easily accessible on-line adjusting of the position of those flow
control elements 10 in relation to the outlet pipes 111. For
example, as shown in FIG. 2A, the flow control elements 10 may each
be connected to and supported by a straight support rod 21 which in
turn is supported by and mounted in sealed bushings 22 on the
discharge turret 108. In this configuration, individually adjusting
each straight support rod 21 by sliding it back and forth or
rotating it causes a change in the position of the corresponding
flow control element 10 inside the discharge turret 108, thereby
resulting in a shift in coal flow to the outlet pipe 111.
Similarly, FIG. 2B illustrates the adjustment mechanism 20 in which
the each flow control element 10 is connected to and supported by
an orthogonal support rod 21. The orthodongal support rod 21 is
supported by and mounted in bushings 22. Again, individually
adjusting the orthogonal support rods 21 by sliding them back and
forth or rotating them within the bushings 22 causes a change in
the position of the corresponding flow control element 10 inside
the discharge turret 108, thereby resulting in a shift in coal flow
to the outlet pipe 111.
[0033] The shape and dimensions of the flow control elements 10 and
the distance between the flow control elements 10 and the outlet
pipes 111 are important parameters in outfitting a particular coal
pulverizer with the present invention. Specifically, the flow
control elements 10 must be positioned within the discharge turret
108 a sufficient predetermined distance from the pulverized coal
outlet pipes 111 such that they have a negligible effect on the
distribution of primary air flow while coincidentally having a
significant effect on the distribution of pulverized coal. The
primary air flow distribution 116 should not be disturbed because
in most boilers primary air flow is balanced by the use of
orifice-type restrictors in the individual pulverized coal outlet
pipes 111. Thus, if primary air flow distribution 116 was
disturbed, air flow would have to be re-balanced whenever a flow
control element 10 was adjusted. The shape of the flow control
elements 10 likewise affects the distribution of primary air
flow.
[0034] To determine the preferred shape of the flow control
elements 10 and the preferred distance from the entrance 112 to
pulverized coal outlet pipe 111 to position the flow control
elements 10, the inventors conducted a series of quantitative
experiments. These experiments were conducted on a laboratory scale
pressurized vertical spindle mill type pulverizer having four
outlet pipes and configured with air foil shaped flow control
elements 10 (as shown in FIGS. 3A-B and 4). During the experiments
both the distribution of pulverized coal into the individual
pulverized coal outlet pipes 111 and primary air flow was
monitored. The results indicated that positioning the flow control
elements within the discharge turret at a distance upstream of the
entrance 112 to the pulverized coal outlet pipes approximately
equal to two times the outlet pipe diameter 117 induces a wide
downstream pulverized coal flow wake 115 relative to the primary
air flow distribution wake 116, thereby providing an efficient
method for controlling the distribution of pulverized coal flows
among the outlet pipes while having a negligible effect on air flow
distribution.
[0035] Additionally, referring to FIG. 4, these experiments
indicated that flow control elements 10 having a streamlined
cross-section comprising a convex, rounded windward end 11, smooth
tapering sides 12 and a pointed leeward end 13 (i.e. an air foil
shape), wherein the diameter of the rounded windward end 11 is
approximately equal to one-quarter the diameter 117 of the
pulverized coal outlet pipe 111 and the length of the flow control
element 10 is approximately equal to one half the diameter 117 of
the pulverized coal outlet pipe 111, were found to provide close
control over the distribution of pulverized coal flow with
negligible impact on air flow distribution. This streamlined design
allows both the pulverized coal and air to flow easily over the
flow control elements 10 towards the outlet pipes 11. The flow of
coal over this streamlined shape creates a wider coal particle
concentration wake 115 than that of the primary air flow wake 115.
In other words, the effect to the primary air flow is negligible.
It should be understood to one skilled in the art that other
streamlined configurations for the flow control elements will
suffice and provide similar satisfactory results.
[0036] Therefore, in order to practice the method of the present
invention and configure the device of the present invention to a
particular pulverizer the distance of the flow control elements 10
from the outlet pipes 111 and the dimensions and cross sectional
shape of the flow control elements 10 should be predetermined by
testing and cataloging the results for that pulverizer, or by a
more refined mathematical approach based upon the results of the
experiments herein describe, in light of the different dimensions
and internal configuration of the particular pulverizer. However,
based upon the above-described experiments a user should start with
a streamlined coal flow element with a frontal diameter and length
of one quarter and one half, respectively, of the diameter of the
outlet pipes. The flow control element should be positioned a
distance upstream from the outlet pipes within the discharge turret
of approximately twice the diameter of the outlet pipes. Then, this
configuration should be subjected to trial-and-error
adjustments.
[0037] One skilled in the art will appreciate that while the
above-described positioning of the flow control elements and the
shape and dimensions of the flow control elements were made with
reference to a pressurized vertical spindle pulverizer with four
pulverized coal outlet pipes, depending on the configuration of the
particular pulverizer, a variety of flow control element positions
and flow control element shapes and dimensions are considered to be
within the scope and spirit of the present invention.
[0038] For example, one skilled in the art will recognize that for
a vertical spindle pulverizer with three outlet pipes, the spacing
between outlet pipes is greater than with a four outlet pipe
pulverizer and thus the distance between the entrance to the outlet
pipes and the flow control elements and the shape and dimensions of
the flow control elements might require adjusting in order to
minimize the effect on the distribution of primary air flow while
maximizing the effect on the pulverized coal flow distribution.
Similarly, a coal pulverizer with more than four outlet pipes will
result in less of a physical separation between outlet pipes and
engender further adjustment of the distance between the entrance to
the outlet pipes and the flow control elements and/or the shape and
dimensions of the flow control elements.
[0039] FIG. 5 is a comparative graph of the results of the
above-mentioned experiments showing the percentage of pulverized
coal flow imbalance when the pulverizer was configured both with
and without the flow control elements 10.
[0040] FIG. 6 is a comparative graph of the results of the
above-mentioned experiments showing the effect on primary airflow
distribution when the pulverizer was configured both with and
without the flow control elements 10. As can be seen in FIGS. 5 and
6, a thirty-five percent change in coal flow rate was achieved with
the flow control elements (FIG. 5) while the maximum change in the
primary airflow was less than 5 percent (FIG. 6). Thus, the
individually adjustable flow control elements 10 positioned inside
the discharge turret of the pulverizer 2, will succeed in balancing
the distribution of coal and improving the overall performance via
increased combustion efficiency, decreased unburned carbon in fly
ash, decreased potential for fuel line plugging, burner damage and
furnace slagging, and more uniform heat release within the
combustion chamber. Furthermore, the primary airflow rate in the
individual outlet pipes 111 can be balanced by including fixed
orifice flow restrictors 121 or adjustable orifice flow restrictors
122 inside the outlet pipes 111, as shown in FIGS. 7A and 7B,
respectively. These orifice flow restrictors 121, 122 are
well-known in the art and if used in combination with the
individually adjustable flow control elements 10, boiler operators
will have even greater control over burner balance. The aforesaid
combination is considered to be within the scope and spirit of the
present invention.
[0041] Having now fully set forth the preferred embodiments and
certain modifications of the concept underlying the present
invention, various other embodiments as well as certain variations
and modifications of the embodiments herein shown and described
will obviously occur to those skilled in the art upon becoming
familiar with said underlying concept. It is to be understood,
therefore, that the invention may be practiced otherwise than as
specifically set forth in the appended claims.
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